This invention relates to ink capsules for printing machines and in particular for coding machines.
Coding machines are typically used for printing indicia on articles to indicate, for example: a date of manufacture, an expiry date, prices, numbers relating to the manufacture or packaging of an article etc.. A known coding machine is the applicant""s CC100 coder. The printing head on the coder picks up ink from an ink capsule and prints the indicia on to the article. The ink capsule typically includes an ink retaining pad which is conventionally made from felt. The use of felt works well with conventional solvent based links in which the solvent is typically ethyl alcohol. However solvent based processes are no longer considered desirable in that the solvent creates an unsuitable work environment and the waste products from the process are environmentally unfriendly.
In view of the above problems there is now a trend towards the use of water based printing mediums. Another advantage of water based codes, is that they can, if desired, be removed by washing prior to sale of the marked goods.
The use of an aqueous medium allows for the use of a wide range of different coloured inks, in particular inks which are coloured by the use of pigments. The use of pigmented inks has given rise to problems in that the felt pads filter out the pigment particles. Furthermore, if an alternative ink retentive material is substituted for the felt, the ink capsule tends to leak since in use the face of the ink capsule is generally vertical and the aqueous based inks are not self-sealing, unlike solvent based inks. This may cause an unsightly mess on the article being printed.
The present invention provides an ink capsule for use with aqueous pigmented inks without the above problems.
According to the present invention there is provided an ink capsule for a printer, which comprises a container having a hollow shell with a mouth and an inlet port through the container shell, a flexible impermeable liner sealed to the container shell, the container and liner being filled with a resilient polymeric foam, and the mouth of the container being closed by a porous closure.
The container may be moulded from a suitable plastics material such as a polyolefin, preferably polyethylene in particular a high density polyethylene.
The liner is thin and pliable and is formed form resilient readily deformable material such as an elastomer, for example natural rubber, butyl rubber, nitrile rubber etc., or a laminate of different elastomers. A natural rubber latex has been found particularly suitable. The porous disc is preferably a sintered polymer, more preferably a fluoropolymer.
The foam, which in use retains the ink, is preferably an open cell material such as polyethylene foam, or a polyurethane foam in particular a polyether foam.
The invention also relates to an ink supply for a printer, which includes an ink capsule according to the invention, wherein the supply includes a variable volume fluid reservoir connected to the inlet port of the container allowing for the movement of fluid between the reservoir and the container in response to the expansion and contraction of the reservoir.
Movement of fluid into the container squeezes the foam within the liner forcing ink through the porous closure to be transposed to the printing head, and movement of fluid from the container causes the foam to expand, sucking the excess ink back into the container.
Preferably the reservoir comprises a cylinder having a piston reciprocable therein to displace fluid, being resiliently biased to an equilibrium condition of maximum volume.
The maximum stroke of the piston is adjustable to control the squeeze on the foam in the container by varying the volume of fluid displaced. The squeeze on the foam may alternatively, or additionally, also be adjusted by controlled bleed-off of the fluid displaced.
According to yet another aspect of the invention there is provided a printing machine having an ink supply system as described above for a printing head, wherein the printing head is operated by a pneumatic cylinder which is connected to the reservoir so that a pulse of air pressure to the pneumatic cylinder also pushes fluid into the container.